Oilseeds are grains that are valuable for the oil content they produce. Some of these oilseeds include (but are not limited to) cotton seeds, rapeseeds, mustard, sunflower, safflower, tobacco seeds, sesame soybeans, cotton seed, flaxseed, and canola seed. The oil content in these seeds depends on the type of plants, but it is common to get 15-50 weight % of oil in the total seed mass. Table 1 shows the oil content in some common seeds on a dry basis:
TABLE 1MoistureOil/FatcontentcontentSeeds(wt %)(wt %)Cotton515-25Rape940-45Mustard725-45Sesame525-50Sunflower525-50Safflower525-30Tobacco735-45
Oilseeds are used chiefly to produce vegetable oil and oilseed meal, which in turn are used to produce food fats and oil products, as well as animal feed for poultry, hogs, and cattle. Other applications are in soap-making, cosmetics, detergents, or as an ingredient in other foods.
Recently, non-food based oils (e.g., tobacco seeds, cotton seeds) have been envisioned as a renewable feedstock for producing biodiesel or other alternative fuels. The procedures to extract oil from seeds are generally solvent extraction and pressing. At commercial scales, the seeds are subjected to a number of processing steps prior to oil extraction. The oilseed is first cleaned to remove trash, dirt, and sand before subjecting the oilseeds to mechanical extraction such as pressing or solvent extraction process. The conventional method of pressing the seeds leaves too much high value oil in the seed cakes. Therefore, solvent extraction methods are used to maximize the oil extracted.
Solvent extraction achieves more complete oil recovery than mechanical extraction but requires a thorough preparation of the feedstock (e.g. drying, cleaning, dehulling, conditioning, flaking, cooking/tempering, pre-pressing, etc.) Solvent extraction removes the oil from a flaked seed or oil-cake by treating the flaked seed or oil-cake with non-polar solvents such as hexane. FIGS. 1A and 1B illustrate the major steps involved in oil extraction using pressing and solvent extraction. These processes are generally expensive and have some well-known challenges, such as additional seed preparation stages, use of dry seeds, primer pressing, steam cooking to facilitate the solvent extraction process, long extraction time, loss of volatile compounds, and the generation of large amount of toxic solvent/chemical waste. Accordingly, improved processes are desired.